batch_auto_20260713 202607131256465730 BOEM ESP geoESPIS ESPIS@boem.gov Bureau of Ocean Energy Management Are expanding Pink Salmon populations in the Arctic produced from regional watersheds? University of Alaska Fairbanks University of Alaska Fairbanks The Arctic is experiencing rapid environmental changes that appear to be associated with the poleward expansion of sub-Arctic fish populations into the region. Pink salmon (Oncorhynchus gorbuscha) are an important species in many coastal marine ecosystems of Alaska and the species has been increasingly observed in Alaskan Arctic watersheds. Whether returning adult Arctic pink salmon are produced locally or originate from outside the region remains an important, yet unresolved topic of debate. The objective of this project was to use otolith geochemistry to determine if adult pink salmon captured in the Arctic originated from local waters. Water and otolith samples collected in the Alaskan Arctic, northwest Alaska, and Prince William Sound in 2020 and 2021 were analyzed for 87Sr/86Sr isotopes, Sr/Ca and Ba/Ca concentrations, as well as stable delta-O-18 and delta-C-13 isotopes. Based on water chemistry, 87Sr/86Sr was the most discriminative geochemical marker for determining the provenance of pink salmon in this study. Results indicate that the majority (65%) of adult pink salmon sampled in the Alaskan Arctic likely did not originate from the region, however, for a proportion of fish (35%) Arctic origin could not be ruled out. Results suggest that there may be establishing populations reproducing successfully in the Arctic. Strontium isotopic ratios in the freshwater portion of the otolith were highly variable between individuals both within and across populations, reflecting life history diversity which is an important consideration in future geochemical studies of salmon otoliths. Multivariate analyses suggested that Arctic Alaska pink salmon populations were more variable in otolith core and early ocean delta-O-18 and delta-C-13 isotopic areas than Prince William Sound pink salmon populations, supporting our conclusion that pink salmon collected in the Arctic are likely of multiple origins. Further, a hierarchical cluster analysis suggests some course-scale clustering of Arctic and Prince William Sound pink salmon separately, which we interpret to indicate that pink salmon sampled in Arctic watersheds are perhaps strays from some similar source population outside of the Arctic region. Refining tools to better understand the use of Arctic habitat by pink salmon is critical for developing mitigation and management measures. 351056 U.S. Department of the Interior, Bureau of Ocean Energy Management, Environmental Studies Program https://doi.org/10.13039/100012475 M20AC10013 10.67297/9A1E5C https://boem.gov/awardpages/100316